Biological aging at the molecular level is imperfectly understood. Collagen and proteoglycan of tendon will be considered as molecules that are programmed genetically regarding aging and these biopolymers will be assumed as indices of the biological aging process. The prime aim of this research will be to measure the interrelationship of these molecules directly in tendon without chemical or physical disruption. The anticipated changes will be correlated with normative aging, and with retarded or accelerated aging in rats as a function of varying nutrition. Luminescent probing will be used for direct observation in tendon preparations. Information will arise from assessment of ultraviolet light activated electron excited states (principally triplet, or as phosphorescence) of tail tendons supercooled to 77 and 4.2 degrees Kelvin. The unique luminescent domains to be optically quantified and differentiated should be found in collagen as tyrosyl residues in polypeptide chains, and in proteoglycan as tryptophanyl residues. These aromatic amino acids are known to differ significantly in electron excited states. A fully compensated, low-temperature spectrophotofluorometer will be modified to handle tendon fibers. Optical data from the instrument will be fed to a computer which will then discern and denote changes due to aging as quantum functions in terms of initial population of excited states and their lifetimes.